Hi team. I've got a 5.0 XKR that has non-original mufflers on the rear. I've found a 4.2 XKR muffler locally which would help me get the rear looking a bit more stock again. I understand that the piping going to the muffler is different between engines due to the active differential on the 5.0. If I modified that, is there anything else I would need to worry about? Is the 4.2 any smaller/quieter than a standard 5.0 backbox?

More than likely I'll do some surgery to increase the noise a bit while maintaining the look. But want to fundamentally know if it will drop in besides the aforementioned.

 

Think they’re the same, other than the input pipes, haven’t read of any differences.

 

To the best of my knowledge, no one on this Forum has ever fitted a 4.2L XKR muffler on a 5.0L XKR. As this old thread explains, there's only one way to find out. Since there are many physical differences between them, chassis mods will be required to make the 4.2L.muffler fit the 5.0L. Anything's possible with enough $$$. See:
Convert 4.2L exhaust to fit 5.0L.

I prefer the 4.2L XKR exhaust sound, which has a sophisticated high pitch as RPMs increase - than the 5.0L XKR with the Performance Active Exhaust (X-pipe), which sounds like a 5.0L Shelby Mustang.

Control over the active exhaust valve depends on throttle position and RPMs. When closed, the exhaust is very quiet. That's why many XKR owners permanently removed Fuse 19 in the fuse box behind the rear seat in order to keep the valve open at all times.

There are lots of XKR exhaust videos on YouTube, including custom exhausts from a variety of manufacturers. Watching them all is exhausting.

Sorry, couldn't rest.

 

Thanks guys. I have a pre 2012 5.0 so who knows! Might have the correct hanger mounts. I'll try and see how close it comes to fitting first and decide if it's going to be too painful or not. I'm definitely not going to modify the chassis to accept the backbox but would like an OEM alternative to my current setup. Hard to get spares/wrecked things in NZ...

 

See post #32 in this thread:
XK Backbox
Putting a 5.0 XKR backbox on a 4.2 XK, the poster didn’t say the hangers needed modification. So you should be able to easily do the reverse.

 

Thanks for the find. I picked up the 4.2 XKR muffler today. I measured the factory hanger points on the body and on the muffler itself. Good news is that they line up! I measured 'east to west' mounts and the distance between the rear mount and each of the side mounts. East to west is roughly 1060mm long and centre to side mount is 630mm. I have a 2010 5.0 XKR and the mounts on the body are bolt on, not welded.

Next step is to drop the old exhaust and make sure the hangers do 100% work. Then I'll do some surgery on the box to a) see what's in it and b) hopefully increase the tone a bit. Then the final step is modifying the entry into the exhaust to work for a 5.0 diff. Hopefully in the future this info is useful to someone!